Blood flow in patient's extremities, particularly the legs, markedly decreases during extended terms of confinement. Such pooling or stasis is particularly acute in surgery and during recovery periods immediately thereafter.
Blood flow compressive devices, such as shown in U.S. Pat. Nos. 4,013,069 and 4,030,488 develop and facilitate the application of compressive pressures against a patient's limb and in so doing promote venous return. The devices comprise a pair of sleeves which are wrapped about the patient's limbs, with a controller for supplying the pressurized fluid to the sleeves. Such sleeve devices are disclosed in U.S. Pat. Nos. 4,402,312 and 4,320,746.
One use for the above-mentioned devices is the prevention of deep venous thrombosis (DVT) which sometimes occurs in surgical patients when they are confined to bed. When a DVT occurs, the valves that are located within the veins of the leg can be damaged which in turn can cause stasis and high pressure in the veins of the lower leg. Patients who have this condition often have leg swelling (edema) and tissue breakdown (venous stasis ulcer) in the lower leg.
In a known controller, fluid supplied by the controller to the sleeves is generated by a piston compressor, and the flow is controlled by a flow control valve which is part of a separate flow control assembly to provide intended flow and pressure to the sleeves. The separate flow control assembly adds to the complexity and cost of the equipment. The size and weight of the equipment is also affected by the presence of the flow control assembly and the linear piston compressor typically employed.
In U.S. Pat. No. 5,031,604 a controller for applying compressive pressure to a patient's limb employs a linear oscillator compressor driven by a pulse signal the number of which is adjusted to energize and de-energize the compressor to provided intended output pressure. Feedback pressure control is employed using a pressure sensor.